Can I add the output of the VSE as input to the node diagram?
There is an addon to send VSE strips to the compositor:

http://blenderartists.org/forum/attachment.php?attachmentid=262986&amp;d=1380892092

The selected video strips will show as image nodes on the compositor and then the resulting composition gets sent back as a new video strip to the VSE.

A video tutorial on how to use it is here:
https://www.youtube.com/watch?v=fiDlNm9iJs4